The present invention is related to techniques of determining a path in DWDM networks.
DWDM (Dense WDM) networks are optical networks in which optical signals at different wavelengths share an optical fiber. Each wavelength defines a particular communication channel. In a stricter sense, DWDM also refers to an ITU (International Telecommunications Union) standard which includes the specification of the particular channel wavelengths and the spacings between these channels and is based upon WDM (Wavelength Division Multiplexing), an earlier ITU standard in which the channel spacings were further apart and a smaller number of wavelength channels were carried by an optical fiber. It should be noted that the term DWDM, as used herein, refers to the first, more inclusive sense so as to include the ITU WDM and DWDM standards, unless specifically stated otherwise.
For communication to be established between the source of the communication and its destination in a network, a path must be selected through the network nodes. The network path is determined by the control plane of the network. At each network node there is a control unit which, linked to other control units at other nodes of the network, selects the path of a communication from the node. The aggregate of the control units form the control plane of the network which, after determining the path, sets up the path of a communication from its source to its destination through the network nodes. Common technologies for such path determination are, e.g., IP (Internet Protocol), Frame Relay, ATM (Asynchronous Transfer Mode) and Ethernet, and a technology which fits over such older technologies is MPLS (MultiProtocol Label Switching) and its latest version GMPLS (Generalized MPLS). An emerging standard is PCE (Path Computation Engine) by which a server computes a path through the network.
These electronic control plane technologies are adapted for electronic networks. But unlike electronic networks, not only must the physical path of the communication through a DWDM network be determined, but also its wavelength. Furthermore, the nature of the optical signals requires that optical parameters, e.g., the attenuation, chromatic dispersion between the nodes and the like, be considered in the proper selection of an optical path to ensure that signals reach their intended destination in proper condition. Otherwise, the optical signals must be regenerated at one or more intermediate nodes between source and destination.
Control planes of proposed optical networks either do not appear to have considered the problems and requirements of routing a communication through an optical network without regeneration, or the nodes of the proposed network are packed with optical parametric information so that each node can properly calculate the routing connections. In such cases, the processors at the nodes often require so much computing power and time to process the complex routing algorithms that routing operations are slowed. The result is that either the problem of optical networks is ignored completely or the proposed solution adversely affects the operations of the network.
The present invention provides for optical control planes which while highly suitable for routing a communication through an optical network, are easily adaptable with electronic control planes.